Sound absorbing material



i Dec.'5, 1933. T. c. HOWARD 1,937,889

SOUND ABSORBING MATERIAL Filed Oct. 6. 1931 yan Patented Dec. 5, 1933 'Y UNITED s'rarlzsA PATENT OFFICE 5 Claims.

This invention relates to an improvement in sound absorbing materials, particularly masonry or composition tiles or the like which depend for their acoustic properties upon porosity. Such materials may be employed as wall or ceiling covering or wherever it is desired to provide a sound absorbing surface.

While materials of a porous nature have heretofore been used it has been found that the painting or other coating of the exposed surface provides a film of coating material, which, unless the treatment is carefully applied, closes the exposed pores and thereby greatly impairs the acoustic properties of the material. If the coating material is suiiicently light in body, as for example a paint of water-like consistency, no damage will result but, in actual practice, experience has shown that painters can not be rellied upon to treat the acoustic materials properly particularly when redecorating. The result is that a demand has arisen for sound absorbing materials which can be restored to their original acoustic condition if improperly treated.

Holes, usually cylindrical, have heretofore been made through or in the exposed surfaces of the material to overcome this difficulty, the walls of such holes providing sound absorbing surfaces, and in order to avoid marring the appearance of the finished surfaces the holes are generally made small, one sixteenth or three thirty-seconds of an inch in diameter. If, however, the surfaces are coated so that the coating film extends over and closes ,themouths of the holes, the sound waves are prevented from entering and implnging upon the walls of the holes. While such films may be removed, as by an air gun, or, if regularly spaced, by a gang punch, this operation has a tendency to carry the film into the holes, thereby partially at least coating the walls of the holes and reducing the sound absorbing properties.

When the holes are cylindrical throughout and of a larger diameter, as for example one-quarter of an inch, thepaint or other coating may be worked into them by the brush or spray. In other Words, if the holes are cylindrical and of a small diameter there is a tendency to form films over the mouths and if the holes are cylindrical and of a large diameter,` the paint enters and coats the Walls thereof.

The primary object of this invention is to provide sound absorbing materials having holes small in diameter at the mouths, extending inwardly from the exposed surfaces wholly or partially through the materials. Such holes following thev usual practice may be one-sixteenth or three thirty-seconds of an inch in diameter at the exposed surfaces but are so formed that any film formed over the mouths of the holes by the coating of the surfaces may be removed from the mouths of the holes Without coating the walls of the holes. More specifically the holes taper inwardly so that the walls thereof diverge from the exposed surfaces, thus providing absorption surfaces which approach in area and effectiveness the surfaces provided by cylindrical holes larger in diameter and, at the same time, avoiding the disadvantage in appearance of the larger holes.

Further objects of the invention will be apparent from a consideration of the following description and of the accompanying drawing, in which:

Fig. 1 -is a fragmentary front elevation of a structure including acoustic materials made in accordance with this invention;

Figs. 2 and 3 are front and rear elevations respectively of one unitof such material; and

Fig. 4 is an enlarged sectional View taken through the structure illustrated in Fig. 1, in combination with a gang punch for cleaning the mouths of the holes in the acoustic material, by removing therefrom any hole-closing film which might result from coating the surface or otherw1se.

The structure illustrated in Fig. 1 comprises a plurality of tiles 10 of masonry or other porous composition and a backing 11. The backing 11 may be supported in any suitable manner in position and the tiles l10 cemented or otherwise secured thereto or the tiles may be suitably supported and the backing attached tothe rear surfaces or under certain conditions, as will be pointed out below, the backing may be omitted. The outer surfaces of the tiles are preferably painted, glazed, enameled, or similarly treated to giveI a pleasing finish to the structure, which treatment forms an outer coating or film 12.

As pointed out above, if the coating film 12 extends over and closes the pores, the .acoustic properties of the tiles, in so far as they depend upon their porosity, are partially or completely destroyed. In order to restore such properties the tiles are perforated with holes 15, the walls of which are porous and absorb to a considerable extent the sound Waves which impinge thereon. The area at the mouths of the holes is relatively small so that the presence of the holes does not detract from the appearance of the finished structure. The walls of the holes taper inwardly from the mouths and the areas of the successive cross sections increase rapidly as will be apparent from a consideration of Fig. 4. It is well known that the absorption of the lateral component of sound waves is particularly effective and by tapering the walls the absorptive properties of the holes are increased Without enlarging the mouths of the holes so that such holes approach in effectiveness to holes of a larger uniform diameter throughout. In the illustratedV embodiment the holes are bored or pressed with instrumentalities so formed or manipulated that each hole comprises a cylindrical portion 16 and a conical portion 17, the apex of the latter portion piercing the outer surface to form the mouth 18.

If, as a result of the coating treatment, the mouths of some or all of the holes are closed with a film this must be ruptured in order that the tiles should exercise their full acoustic properties. One way of performing this operation is by means of a gang punch 20 having a plurality of pins 2l suitably spaced so that a number of holes are treated simultaneously. These pins are of such dimensions that they will clear the entire mouths of the holes. Since the mouths are defined by a sharp edge (see Fig. l4), there is no `possibility that the ruptured films will be wiped by the pins 21 against the walls of the holes and thus reduce their sound absorbing areas.

The particular conformation of the holes 15 shown in the drawing is preferred, but the invention is not limited to such conformation, the essence of the invention being that the holes shall be defined by walls which diverge inwardly from a small aperture in the outer surface to eliminate the danger of smearing the lms against the walls. Similarly the holes may be spaced in any desired manner and the backing 11, which functions, with respect to this invention to prevent the entry of dust or other extraneous matter into the holes or to provide additional absorptive surface, may be of any suitable material or may be omitted if conditions are such as to render it unnecessary.

I claim: K

1. A unit of sound absorbing material having a plurality of holes therein the Walls of which terminate, at the exposed surface of said unit, in apertures of small area and diverge inwardly.. therefrom toward the concealed surface of said unit, the apertures in said exposed surface being of such small size as not to impair perceptively the appearance of substantial continuity of said exposed surface.

2. A unit of sound absorbing material having a plurality of holes therein the walls of. which terminate, at the exposed surface of said unit, in apertures of small area defined by sharp edges and diverge inwardly therefrom toward the concealed surface of said unit, the apertures in said exposed surface being of such size as not to impair perceptively the appearance of substantial continuity of said exposed surface. y

3. A unit of sound absorbing material having a plurality of holes'therein the Walls of which terminate, at the exposed surface, in apertures of small area and diverge inwardly therefrom toward the concealed 'surface of said unit, the exposed surface of said unit having an appearance of substantial continuity and the surfaces of said wall being porous to absorb the sound vibrations which impinge thereon.

4. A unit of sound absorbing material having a plurality of holes therein the walls of which terminate, at the exposed surface of said unit, in apertures of small area and diverge inwardly therefrom toward the concealed surface of said unit and a coating upon the exposed surface of the unit interrupted at said apertures but providing an appearance of substantial continuity.

5. A unit of sound absorbing material having a plurality of holes therein the Walls of which terminate, at the exposed surface of said unit, in apertures of small area, which holes extend from the exposed surface toward the concealed surface of the unit, said holes being conical at their ends adjacent to the exposed surface of said unit, the apices of such cones piercing the exposed surface and providing openings of such small size as not to impair perceptively the appearance of substantial continuity of the exposed surface.

THOMAS CLARK HOWARD. 

